All optical type wavelength converters are very important devices used to construct advanced wavelength division multiplexing (WDM) networks with flexibility in the future. A specific attention has been paid to wavelength conversion operations using four-wave mixing (FWM) operations within optical fibers, since the wavelength conversion techniques can own very broad wavelength conversion bands, and also can convert multi-channel WDM signals in a batch-manner. The wavelength conversions using the four-wave mixing (FWM) operations within the optical fibers own very wide wavelength conversion bands and can convert wavelength division multiplexing signals for multiple channels in the batch mode. It is, therefore, desirable to provide an improved wavelength converter.